Term Index (I)
Astrophysical terms and names of things beginning with the letter I.
I2
IA
IB
IC
ID
IE
IF
IG
IH
II
IK
IL
IM
IN
IO
IP
IQ
IR
IS
IT
IU
IV
IW
IX
- I (I band): passband for near-infrared light
- I: see IRAS
- I: see Stokes parameters
- I: see double star designation
- I: see state of ionization
- i: see griz photometric system
- i: see ugriz photometric system
- I band: passband for near-infrared light
- I Zw: see Catalog of Galaxies and Clusters of Galaxies
- I Zw 18 (I Zwicky 18): blue compact galaxy with low metallicity
- I Zw 36 (Haro 29): a blue compact galaxy
- I Zwicky 18: blue compact galaxy with low metallicity
- i': see ugriz photometric system
- i-band: see Hubble Ultra-Deep Field
- I2C: see GI2T
- I2T: see GI2T
- IAA (Academia Sinica Institute of Astronomy and Astrophysics): Taiwanese astrophysics research organization
- IAC (Instituto de Astrofísica de Canarias): research institute on Canary Islands
- IACT: see Cherenkov detector
- Iapetus: see Saturn
- moon: a planet's natural satellite, such as Earth's
- IAPPP (International Amateur-Professional Photoelectric Photometry): organization active 1980-2000+
- IAPS (Istituto di Astrofisica e Planetologia Spaziali): Italian astrophysical research institute within INAF
- IAS (Institute for Advanced Study): research institution
- IAS (Istituto di Astrofisica Spaziale): former name of Italian astrophysics research institution
- IASY (International Active Sun Years): 1969-1971 initiative for solar surveys
- IAU (International Astronomical Union): association of professional astronomers
- IAU Circular: see Central Bureau for Astronomical Telegrams
- IAU Circular: see International Astronomical Union
- IAU galactic coordinate system (galactic coordinate system): celestial coordinate system system based upon the galactic plane
- IAU symposium: IAU-sponsored science symposiums
- IAUC: see Central Bureau for Astronomical Telegrams
- IAUC: see International Astronomical Union
- IAUS (IAU symposium): IAU-sponsored science symposiums
- IAYC (International Astronomical Youth Camp): summer camp
- IBAS: see INTEGRAL
- IBEX (Interstellar Boundary Explorer): satellite observing the ISM/heliosphere boundary
- IBEX-Hi: see Interstellar Boundary Explorer
- IBEX-Low: see Interstellar Boundary Explorer
- IBIS: see INTEGRAL
- IBVS (Information Bulletin on Variable Stars): former 1961-2019 publication on variable stars
- IC (Index Catalog): 1895 catalog of galaxies, star clusters, and other nebulae
- IC (Intracluster): region between objects of a cluster such as between stars in a star cluster
- IC 1340: see Cygnus Loop
- IC 342: spiral galaxy in the Council of Giants
- IC 342/Maffei Group: see IC 342
- ICAT (Canadian Institute for Theoretical Astrophysics): national research organization at University of Toronto
- ICC: see InSight
- ICE (International Cometary Explorer): 1980s space mission flying by comets
- ice: solid state of water
- ice giant: planet denser than gas planets and less than rocky planets
- snow line: distance from protostar so cool that water condenses
- superionic ice: odd state of water at high temperature and pressure
- water-ice planet: planet made entirely of water ice
- ice dwarf (plutoid): Pluto-like dwarf planet
- ice giant: planet denser than gas planets and less than rocky planets
- ice line (snow line): distance from protostar so cool that water condenses
- ice: solid state of water
- ice transition radius: see snow line
- IceCube: neutrino detector at the South Pole
- IceCube Neutrino Observatory (IceCube): neutrino detector at the South Pole
- IceCube-Gen2: see IceCube
- ICF (ionization correction factor): relations between ion abundances and element abundances
- ICM (intracluster medium): hot plasma throughout a galaxy cluster
- ICQ (International Comet Quarterly): journal regarding comets
- ICRC (International Cosmic Ray Conference): bi-annual cosmic ray conference since 1947
- ICRF: celestial reference frame based upon quasars
- ICRF1: see ICRF
- ICRF2: see ICRF
- ICRF3: see ICRF
- ICRS (International Celestial Reference System): standardized variation of equatorial coordinate system
- IDA (International Dark-Sky Association): organization promoting control of light pollution
- IDA: see InSight
- IDC: see InSight
- ideal gas: see ideal gas law
- Hayashi limit: limit on the temperature of a star dependent upon its mass and luminosity
- Lane-Emden equation: form of equation of state for gas ball in hydrostatic equilibrium
- ideal gas law: relates pressure, temperature, and volume
- IDEX: see IMAP
- IDFT: see fast Fourier transform
- IDL: interactive vector-oriented programming language
- IDP: see interplanetary medium
- IDS: see Isaac Newton Telescope
- IDS: see Shane Telescope
- IDS: see Washington Double Star Catalog
- IDV: see variable star
- IEEE (Institute of Electrical and Electronics Engineers): professional engineering association
- ITU: international body coordinating communications technology
- IEO: see near-Earth object
- IERS (International Earth Rotation and Reference Systems Service): service monitoring Earth's rotation and precession
- IfA (Institute for Astronomy): U Hawaii astronomy research organization
- IFN (integrated flux nebula): fuzzy illuminated nebula within Milky Way halo
- IFS: see European Southern Observatory Very Large Telescope
- IFS: see SPHERE
- IFS: see integral field spectrograph
- IFTS (imaging Fourier transform spectroscopy): Michelson-interferometer-based imaging spectroscopy
- IFU (integral field unit): instrument to allow a spectrograph to capture data over a 2D field
- IFU Observation
- IFU observation: see integral field unit
- IFU spectroscopy: see integral field unit
- IGAPS: see IPHAS
- IGAS: see Ulysses
- IGM (intergalactic medium): matter between galaxies
- IGR: see INTEGRAL
- IGRINS: see Gemini Observatory
- IGRINS-2: see Gemini Observatory
- IGVV: see Catalogue of Interacting Galaxies
- IGW (internal gravity wave): ripples in a change in density in a fluid
- IGY (International Geophysical Year): 1957-1958 initiative for geophysical and related astronomical research
- IHW (International Halley Watch): initiative to coordinate observation of Halley's Comet in 1986
- II: see state of ionization
- II Zw: see Catalog of Galaxies and Clusters of Galaxies
- III: see state of ionization
- III Zw: see Catalog of Galaxies and Clusters of Galaxies
- IKT: see rare designator prefixes
- illumination: measure of light energy producing a telescope's image
- Illustris Project: 2013-2015 series of cosmological simulations
- IllustrisTNG Project: see Illustris Project
- ILMT (International Liquid Mirror Telescope): 4-meter liquid mirror telescope under construction in India
- iLocator: see Large Binocular Telescope
- ILOM (In-situ Lunar Orientation Measurement): planned experiment to monitor lunar rotation via astrometry from the Moon
- ILOT (intermediate luminosity optical transient): visible-light transient a bit brighter than a nova
- ILR: see Lindblad resonance
- IM (intensity mapping): measure of cosmic matter density
- IM Lup
- MAPS: ALMA survey researching planet-formation
- IM Nor: see T Pyxidis
- IM Normae: see T Pyxidis
- IMACS: see Magellan Telescopes
- PRIMUS: spectrographic survey of galaxies out to redshift 1
- image dissector: see photomultiplier tube
- image dissector photomultiplier: see photomultiplier tube
- image plane (focal plane): plane within optical system at which an image is in focus
- image processing
- Image Reduction and Analysis Facility: NOAO-developed image manipulation/viewing software
- image scale (plate scale): relation between angle and distance across an image
- image slicer: see integral field spectrograph
- image slicer: see integral field unit
- image stabilization: camera mechanism to compensate for movement
- image stacking (stacking): combining images of the same object
- IMAGE: satellite mission to study magnetosphere
- Image-Dissector Scanner: see Shane Telescope
- imager: essentially a word for camera, produces 2D image over some bandwidth
- Imager for Magnetopause-to-Aurora Global Exploration (IMAGE): satellite mission to study magnetosphere
- imaginary number: see complex number
- imaginary part: see complex number
- imaginary unit: see complex number
- imaging
- imaging atmospheric Cherenkov telescope: see Cherenkov detector
- imaging Fourier transform spectrometer: see imaging Fourier transform spectroscopy
- imaging Fourier transform spectroscopy: Michelson-interferometer-based imaging spectroscopy
- imaging spectrograph (imaging spectrometer): device to capture spectrum point-by-point of an image
- imaging spectrometer: device to capture spectrum point-by-point of an image
- spectroscopy: measurement of light with various electromagnetic wavelengths
- Imaging X-ray Polarimetry Explorer (IXPE): space observatory with X-ray polarimeters
- IMAP: future solar science probe
- IMAP-Hi: see IMAP
- IMAP-Lo: see IMAP
- IMAP-Ultra: see IMAP
- IMAPS (Interstellar Medium Absorption Profile Spectrograph): 1980s/1990s UV spectrometer
- IMaX: see SUNRISE
- IMB: 1980s neutrino detector
- IMBH (intermediate-mass black hole): black hole between stellar mass and supermassive
- IMF (initial mass function): function describing initial mass of stars
- IMF: see magnetic field
- immersion grating: grating where light is within the material
- WINERED: near-infrared non-cryogenic spectrograph
- Immirzi parameter: theoretical value relating black hole to its entropy
- IMO (International Meteor Organization): amateur/professional meteor organization
- IMP: see Mars Pathfinder
- IMPACT (International Monitoring Programs for Asteroid and Comet Threat): 1999 IAU-sponsored conference in Italy
- IMPACT: see STEREO
- impact: collision of one solid body with another
- impact erosion: see impact
- impact parameter: see cross section
- impact parameter: see transiting planet
- impacts
- IMPS: see IRAS
- IMRI: see extreme mass ratio inspiral
- IMS: see Giotto
- IMXB: see X-ray binary
- in situ: on site
- in situ observation: see in situ
- In-situ Lunar Orientation Measurement: planned experiment to monitor lunar rotation via astrometry from the Moon
- INAF (Istituto Nazionale di Astrofisica): Italian astrophysical research institute
- INAG (Institut National d'Astronomie et de Geophysique): 1960s-1980s French research institute
- incidence
- inclination (orbital inclination): angle between plane of an orbit and a reference plane
- inclination-type resonance: see orbital resonance
- Index Catalog: 1895 catalog of galaxies, star clusters, and other nebulae
- Index Catalog of Visual Double Stars: see Washington Double Star Catalog
- Index Catalogue of Nebulae and Clusters of Stars (Index Catalog): 1895 catalog of galaxies, star clusters, and other nebulae
- index of refraction (refractive index): measure of how much a material slows down light
- twinkling: blinking, apparent movement and color changes of observed stars
- India
- Indian
- Aditya-L1: 2023 spacecraft viewing Sun and analyzing solar wind
- Indian Initiative in Gravitational-wave Observations: see LIGO-India
- Indian Pulsar Timing Array: group of pulsars timed by the GMRT
- Indian Space Research Organisation: national science and technology agency
- INDIGO: see LIGO-India
- Indus stream
- inelastic scattering: see scattering
- inertia wave (inertial wave): type of wave in a rotating fluid
- inertial forces
- Reynolds number: measure reflecting a fluid system's propensity to turbulence
- inertial frame (inertial reference frame): frame of reference where no force means no acceleration
- inertial frame of reference (inertial reference frame): frame of reference where no force means no acceleration
- inertial mass: see mass
- inertial reference frame: frame of reference where no force means no acceleration
- inertial wave: type of wave in a rotating fluid
- infall
- inferior conjunction: conjunction of an "inferior planet", Venus or Mercury
- inferior planet: see heliocentric system
- infinitesimal transform
- infinitesimal transformation
- inflated gas giant (hot Jupiter): Jupiter-sized gas exoplanet orbiting very close to star
- inflated radii: exceptionally large radii of some hot Jupiters
- inflation: theorized rapid expansion of the very early universe
- inflation field
- inflation theory: see inflation
- inflationary theory: see inflation
- information: see black-hole information paradox
- Information Bulletin on Variable Stars: former 1961-2019 publication on variable stars
- infrared: light with wavelength too long for our eyes to sense
- Infrared Astronomical Satellite (IRAS): 1983 satellite that surveyed the sky in infrared
- infrared astronomy: see infrared
- Infrared Catalog (Two Micron Sky Survey): 1969 infrared catalog produced by Caltech
- infrared cirrus: cirrus-cloud-like infrared emissions from dust, etc.
- infrared dark cloud: molecular cloud not emitting nor transmitting infrared
- infrared excess: more infrared than that of a star's typical spectrum
- Infrared Imaging Surveyor (AKARI): Japanese space infrared telescope
- infrared light (infrared): light with wavelength too long for our eyes to sense
- infrared luminosity: see infrared
- Infrared Optical Telescope Array (IOTA): past optical interferometer in Arizona
- Infrared Processing and Analysis Center (IPAC): Caltech group to collect and analyze infrared observations
- infrared radiation (infrared): light with wavelength too long for our eyes to sense
- Infrared Science Archive (IRSA): archive center for infrared data from NASA missions
- infrared source: astronomical object producing observable infrared
- infrared source: see source
- radio source: astronomical object producing observable radio
- Infrared Space Observatory: 1990s 60-cm infrared space telescope
- Infrared Spatial Interferometer: see Mount Wilson Observatory
- Infrared Survey Facility: 140 cm reflector telescope that images in infrared
- Infrared Telescope Facility (IRTF): Mauna Kea 3-meter infrared telescope
- SpeX: a medium-resolution infrared spectrograph
- InfraRed Telescope in Space (IRTS): 15-cm infrared telescope on Japanese satellite
- Infrared Telescope Maffei: 80 cm infrared telescope in Antarctica
- infrared window: see atmospheric window
- ING (Isaac Newton Group of Telescopes): three telescopes in Canary Islands
- Ingenuity: see Mars 2020
- ingress duration: see transiting planet
- INGRID: see William Herschel Telescope
- initial fluctuation spectrum: the power spectral density of the early universe
- initial fluctuations: early universe density variations leading to current universe
- initial mass function: function describing initial mass of stars
- initiative
- Astro2020: initiative suggesting major survey efforts over the 2020-2030 decade
- Black in Astro: advocacy initiative
- Snowmass: initiative recommending the next decade's particle physics strategy
- INMS: see Cassini
- Inner Cloud (Hills Cloud): cloud of comets and minor planets around the solar system
- inner Lindblad resonance: see Lindblad resonance
- inner Lindblad resonance: see Lindblad torque
- inner moon: see Enceladus
- Inner Oort Cloud (Hills Cloud): cloud of comets and minor planets around the solar system
- inner solar system
- inner working angle: see coronagraph
- inner-Earth object: see near-Earth object
- innermost stable circular orbit: border of region surrounding a BH in which orbits are unstable
- Inouye Solar Telescope (DKIST): 4 m solar telescope at Haleakala Observatory
- InPTA (Indian Pulsar Timing Array): group of pulsars timed by the GMRT
- INS: see neutron star
- InSAR: see synthetic aperture radar
- VERITAS: planned NASA Venus orbiter
- inside-out growth: tendency of galaxy star formation to spread from the center
- InSight: NASA Mars mission to study its interior
- Insight (HXMT): space X-ray observatory launched in 2017
- insolation: solar energy received per unit area in given time
- inspiral: like an orbit that is growing smaller
- inspiral: see orbital decay
- instability region: region around an object where orbits cannot persist
- instability strip: region of H-R diagram where stars are unstable
- instellation: see insolation
- Institut de radioastronomie millimétrique: organized radio astronomy collaboration between France, Germany, and Spain
- Institut für Theoretische Astrophysik (Institute of Theoretical Astrophysics): Heidelberg research institute
- Institut National d'Astronomie et de Geophysique: 1960s-1980s French research institute
- Institute for Advanced Study: research institution
- Institute for Astronomy: U Hawaii astronomy research organization
- Institute for Pale Blue Dots (Carl Sagan Institute): group researching finding life on other planets and moons
- Institute for research on exoplanets: U Montreéal division researching exoplanets
- Institute for Space Astrophysics and Planetology (Istituto di Astrofisica e Planetologia Spaziali): Italian astrophysical research institute within INAF
- Institute for Theoretical and Experimental Physics
- Institute of Astronomy: Cambridge U astronomy research organization
- Institute of Electrical and Electronics Engineers: professional engineering association
- ITU: international body coordinating communications technology
- Institute of Space and Astronautical Science: Japanese national research organization
- Institute of Space and Atmospheric Studies: U Saskatchewan research division
- Institute of Theoretical Astronomy: former Cambridge U astronomy research organization
- Institute of Theoretical Astrophysics: Heidelberg research institute
- Instituto de Astrofísica de Canarias: research institute on Canary Islands
- instrument
- instrument type
- instruments
- INT (Isaac Newton Telescope): 2.5 m telescope in Canary Islands
- INT Galactic Plane Survey: see IPHAS
- INT Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS): H-alpha survey
- INT Photometric Halpha Survey (IPHAS): H-alpha survey
- INTEGRAL: European gamma ray observatory-satellite
- INTEGRAL: see William Herschel Telescope
- INTEGRAL Burst Alert System: see INTEGRAL
- integral field spectrograph: spectrograph that captures images
- data cube: three-dimensional array of numerical data
- integral field spectrometer (integral field spectrograph): spectrograph that captures images
- integral field spectroscopy: see integral field spectrograph
- integral field unit: instrument to allow a spectrograph to capture data over a 2D field
- integrated flux nebula: fuzzy illuminated nebula within Milky Way halo
- integrated Sachs-Wolfe effect: see Sachs-Wolfe effect
- integration time: time spent acquiring a signal
- intensity: power reaching a surface from a specific source
- intensity interferometer: interferometer based upon interference from intensity variations
- intensity interferometry: see intensity interferometer
- Intensity Interferometry at Calern: see GI2T
- intensity map: see intensity mapping
- intensity mapping: measure of cosmic matter density
- intensity mapping experiments (intensity mapping surveys): efforts mapping the intensity of spectral lines across the sky
- intensity mapping surveys: efforts mapping the intensity of spectral lines across the sky
- Inter-University Centre for Astronomy and Astrophysics: initiative promoting astrophysics at Indian universities
- interacting binary: see contact binary
- interacting galaxy: see galaxy interaction
- galactic tide: effect of one galaxy's gravity, such as on another galaxy
- Interactive Data Language (IDL): interactive vector-oriented programming language
- intercloud gas: see interstellar medium
- Interféromètre a 2 Télescopes: see GI2T
- interference: result of interaction of waves
- interference pattern
- interferometer: device detecting EMR properties using interference between waves
- interferometric synthetic aperture radar: see synthetic aperture radar
- VERITAS: planned NASA Venus orbiter
- interferometry: analysis of superimposed EMR waves
- intergalactic dust: dust not within galaxies
- intergalactic HI cloud: cloud of HI not within any galaxy
- intergalactic medium: matter between galaxies
- Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight): NASA Mars mission to study its interior
- interloper: see intensity mapping
- intermediate band: see passband
- intermediate band photometry: see photometry
- intermediate luminosity optical transient: visible-light transient a bit brighter than a nova
- intermediate mass ratio inspiral: see extreme mass ratio inspiral
- intermediate polar: see variable star
- intermediate spiral galaxy: see galaxy classification
- intermediate-mass black hole: black hole between stellar mass and supermassive
- intermediate-mass X-ray binary: see X-ray binary
- intermediate-velocity cloud: see high-velocity cloud
- internal gravity wave: ripples in a change in density in a fluid
- internal wave (internal gravity wave): ripples in a change in density in a fluid
- international
- International Active Sun Years: 1969-1971 initiative for solar surveys
- International Amateur-Professional Photoelectric Photometry: organization active 1980-2000+
- International Astronomical Union: association of professional astronomers
- International Astronomical Youth Camp: summer camp
- International Atomic Time: see Terrestrial Time
- International Celestial Reference Frame (ICRF): celestial reference frame based upon quasars
- International Celestial Reference System: standardized variation of equatorial coordinate system
- International Comet Quarterly: journal regarding comets
- International Cometary Explorer: 1980s space mission flying by comets
- International Coordinate Reference Frame: see International Celestial Reference System
- International Coordinate Reference System: see International Celestial Reference System
- International Cosmic Ray Conference: bi-annual cosmic ray conference since 1947
- International Dark-Sky Association: organization promoting control of light pollution
- International Earth Rotation and Reference Systems Service: service monitoring Earth's rotation and precession
- International Earth Rotation Service (International Earth Rotation and Reference Systems Service): service monitoring Earth's rotation and precession
- International Gamma-ray Astrophysics Laboratory (INTEGRAL): European gamma ray observatory-satellite
- International Geophysical Year: 1957-1958 initiative for geophysical and related astronomical research
- International Halley Watch: initiative to coordinate observation of Halley's Comet in 1986
- International Liquid Mirror Telescope: 4-meter liquid mirror telescope under construction in India
- International Meteor Organization: amateur/professional meteor organization
- International Monitoring Programs for Asteroid and Comet Threat: 1999 IAU-sponsored conference in Italy
- International Occultation Timing Association: volunteer organization to observe occultations
- International Organization for Standardization: standards-development organization
- International Pulsar Timing Array: organization of pulsar timing arrays
- International Quiet Sun Year: 1964-1965 initiative for solar surveys
- International Robotic Antarctic Infrared Telescope (Infrared Telescope Maffei): 80 cm infrared telescope in Antarctica
- International Scientific Optical Network: project to track objects in space
- International Small Telescope Cooperative: former cooperative of small research telescopes
- International Solar Polar Mission (Ulysses): space mission to observe the Sun from off the ecliptic
- International Space Station: long-term manned space station operated by numerous nations
- AMS-02: particle detector on ISS
- COSIE: EUV spectrograph to analyze the corona
- EUSO-SPB: balloon-borne cosmic ray observatory
- MAXI: Japanese X-ray camera on the International Space Station
- NICER: space X-ray mission specifically to view neutron stars
- International Space Year: 1992 initiative re space and astronomy
- International Sun-Earth Explorer: see International Cometary Explorer
- International Supernova Network: SN information sharing initiative
- International System of Units (SI): standardized metric system
- CGS: metric system variant
- International Telecommunication Union (ITU): international body coordinating communications technology
- International Ultraviolet Explorer: 1980s ultraviolet space telescope
- International Variable Star Index: variable star catalog by AAVSO
- International Virtual Observatory Alliance: see virtual observatory
- International Workshop for Astronomy: organization operating the IAYC
- International Workshop on Cometary Astronomy: occasional meeting
- interplanetary dust: see cosmic dust
- interplanetary dust cloud: see cosmic dust
- interplanetary dust particle: see interplanetary medium
- interplanetary magnetic field: see magnetic field
- interplanetary medium: matter in the solar system around and between planets
- Interplanetary Physics Laboratory (Wind): spacecraft measuring solar wind
- interplanetary scintillation: see scintillometry
- Interplanetary Scintillation Array: UK radio telescope that first detected pulsars
- interpretation
- CO to H2 factor: assumed ratio between observed CO emission lines and H2 mass
- interstellar astronomy (interstellar astrophysics): astronomy of the ISM including dust and clouds
- interstellar astrophysics: astronomy of the ISM including dust and clouds
- Interstellar Boundary Explorer: satellite observing the ISM/heliosphere boundary
- interstellar cloud (cloud): higher-density region of space
- interstellar dust: see cosmic dust
- interstellar extinction: see extinction
- interstellar holography: holographic analysis of incoming EMR to study the intervening ISM
- interstellar magnetic field: galactic magnetic field between that of stars
- Interstellar Mapping and Acceleration Probe (IMAP): future solar science probe
- interstellar matter (interstellar medium): matter within a galaxy between star systems
- interstellar medium: matter within a galaxy between star systems
- Interstellar Medium Absorption Profile Spectrograph: 1980s/1990s UV spectrometer
- interstellar planet (free-floating planet): planet that is not orbiting a star
- interstellar planet: see field
- interstellar radiation field: EMR throughout the "empty" space of a galaxy
- interstellar reddening (reddening): red appearance of astronomical objects because blue light is attenuated by dust
- interstellar scintillation: see scintillometry
- intertropical convergence zone: circulation pattern near equator where north and south Hadley cells meet
- Intracluster: region between objects of a cluster such as between stars in a star cluster
- intracluster gas (intracluster medium): hot plasma throughout a galaxy cluster
- intracluster medium: hot plasma throughout a galaxy cluster
- intraday variable: see variable star
- intrinsic color index: see color index
- intrinsic S-star: see S-type star
- intrinsic variable: see variable star
- inverse beta decay: see beta decay
- inverse bremsstrahlung: see bremsstrahlung
- inverse Compton: see Compton scattering
- inverse Compton scattering: see Compton scattering
- inverse discrete Fourier transform: see fast Fourier transform
- inverse Fourier transform: see Fourier transform
- Fourier series: type of series able to approximate a periodic function
- inverse model: see forward model
- retrieval: determining parameters through observation and modeling
- Tau-REx: spectral line retrieval code for exoplanet atmospheres
- inverse Radon transform: see tomography
- inverse square law: a value's dependency upon reciprocal of the square of the distance from something
- inverse volume weighting (volume weighting): method of accommodating the Malmquist bias
- Io: well-known Jupiter moon
- Io plasma torus: see Io
- Io torus: see Io
- IO:I: see Liverpool Telescope
- IO:O: see Liverpool Telescope
- IoA (Institute of Astronomy): Cambridge U astronomy research organization
- IOK: see rare designator prefixes
- ion: non-neutral atom or molecule, with missing or extra electrons
- ion engine: type of electrical spacecraft engine
- Dawn: explorer spacecraft sent to asteroids Vesta and Ceres
- ion thruster (ion engine): type of electrical spacecraft engine
- ionic bond: see ion
- ionic ocean: see zonal flow
- ionization (state of ionization): difference in an ion's electron count versus proton count
- ionization chamber
- ionization correction factor: relations between ion abundances and element abundances
- ionization energy (ionization potential): energy needed to ionize an atom
- ionization fraction: a substance's ratio of unattached electrons to nuclei
- ionization front
- ionization potential: energy needed to ionize an atom
- ionization state
- ionization temperature: see temperature
- ionization valve (kappa mechanism): stellar instability caused by opacity increasing with temperature
- ionize: see state of ionization
- ionized carbon fine structure line: carbon line that traces distant star formation
- ionized carbon forbidden line (ionized carbon fine structure line): carbon line that traces distant star formation
- ionized hydrogen: state of hydrogen when sufficiently hot
- ionized interstellar medium
- ionizing photon: see ionizing radiation
- ionizing radiation: radiation with photon energy sufficient to ionize
- ionosphere: layers of Earth atmosphere with significant ions
- space weather: varying conditions in space affecting Earth and humans
- ions
- ioschrone
- IOTA: past optical interferometer in Arizona
- IOTA (International Occultation Timing Association): volunteer organization to observe occultations
- IPAC: Caltech group to collect and analyze infrared observations
- IPC: see HEAO-2
- IPHAS: H-alpha survey
- IPHASX: see IPHAS
- IPM (interplanetary medium): matter in the solar system around and between planets
- IPMO (free-floating planet): planet that is not orbiting a star
- IPMO: see planetary mass object
- IPS: see scintillometry
- IPS Array (Interplanetary Scintillation Array): UK radio telescope that first detected pulsars
- IPTA (International Pulsar Timing Array): organization of pulsar timing arrays
- IPTA+: see International Pulsar Timing Array
- iPTF: see Palomar Transient Factory
- IQSY (International Quiet Sun Year): 1964-1965 initiative for solar surveys
- IR (infrared): light with wavelength too long for our eyes to sense
- IR excess (infrared excess): more infrared than that of a star's typical spectrum
- IR SFR: see star formation rate
- IR source: see source
- radio source: astronomical object producing observable radio
- IR star formation rate: see star formation rate
- IRAC: see Spitzer Space Telescope
- IRAC Shallow Cluster Survey: see IRAC Shallow Survey
- IRAC Shallow Survey: Spitzer survey of moderately wide field
- IRAF (Image Reduction and Analysis Facility): NOAO-developed image manipulation/viewing software
- IRAIT (Infrared Telescope Maffei): 80 cm infrared telescope in Antarctica
- IRAM (Institut de radioastronomie millimétrique): organized radio astronomy collaboration between France, Germany, and Spain
- IRAM 30m Millimeter Radio Telescope (IRAM 30m Telescope): millimeter-range radio telescope in Sierra Nevada, Spain
- IRAM 30m Telescope: millimeter-range radio telescope in Sierra Nevada, Spain
- IRAS: 1983 satellite that surveyed the sky in infrared
- GOALS: across-spectrum observation of 200 LIRGs
- IRAS 13224-3809: active Seyfert galaxy with well-studied SMBH
- IRAS 16293-2422
- IRAS 22134+5834
- IRAS F: see IRAS
- IRAS Faint Source Catalog: see IRAS
- IRAS Minor Planet Survey: see IRAS
- IRAS Point Source Catalog: see IRAS
- IRAS-FSC: see IRAS
- IRAS-PSC: see IRAS
- IRC (Two Micron Sky Survey): 1969 infrared catalog produced by Caltech
- IRC: see AKARI
- IRc: see rare designator prefixes
- IRCAM: see United Kingdom Infrared Telescope
- IRCS: see Subaru Telescope
- IRD: see Subaru Telescope
- IRDC (infrared dark cloud): molecular cloud not emitting nor transmitting infrared
- IRDC: see rare designator prefixes
- IRDIS: see European Southern Observatory Very Large Telescope
- IRDIS: see SPHERE
- IREM: see INTEGRAL
- iREX (Institute for research on exoplanets): U Montreéal division researching exoplanets
- iridium
- IRIS (AKARI): Japanese space infrared telescope
- IRIS: see Thirty Meter Telescope
- IRIS: see Voyager
- IRIS2: see Anglo-Australian Telescope
- IRMS: see Thirty Meter Telescope
- iron: metal, Fe, atomic number 26
- iron core collapse: see core collapse
- iron Kα (K-line): iron X-ray line
- iron K-line (K-line): iron X-ray line
- iron line (K-line): iron X-ray line
- iron peak: peak in the distribution of abundances surrounding iron
- iron peak element: element near the iron peak
- iron star: see exotic star
- iron-56
- nickel: metal, Ni, atomic number 28
- IRPOL: see United Kingdom Infrared Telescope
- Irr-I: see irregular galaxy
- Irr-II: see irregular galaxy
- irradiance: EMR power reaching a surface
- irregular
- irregular galaxy: galaxy that's not a disk or ellipsoid
- irregular moon: moon with an atypical orbit, such as retrograde
- irregular satellite (irregular moon): moon with an atypical orbit, such as retrograde
- irregular variable: see variable star
- IRS (infrared source): astronomical object producing observable infrared
- IRS: see Spitzer Space Telescope
- IRS: see infrared
- IRSA: archive center for infrared data from NASA missions
- IRSF (Infrared Survey Facility): 140 cm reflector telescope that images in infrared
- IRSPEC: see New Technology Telescope
- IRSV: see rare designator prefixes
- IRT: see THESEUS
- IRTF: Mauna Kea 3-meter infrared telescope
- IRTS: 15-cm infrared telescope on Japanese satellite
- Irvine-Michigan-Brookhaven detector (IMB): 1980s neutrino detector
- IRX (infrared excess): more infrared than that of a star's typical spectrum
- IS☉IS-EPI: see Parker Solar Probe
- ISAAC: see European Southern Observatory Very Large Telescope
- Isaac Newton Group of Telescopes: three telescopes in Canary Islands
- Isaac Newton Telescope: 2.5 m telescope in Canary Islands
- iSALE: code modeling the shock physics of impacts
- ISAMS: see Upper Atmosphere Research Satellite
- ISAS (Institute of Space and Astronautical Science): Japanese national research organization
- ISAS (Institute of Space and Atmospheric Studies): U Saskatchewan research division
- ISCO (innermost stable circular orbit): border of region surrounding a BH in which orbits are unstable
- ISCO-radius: see innermost stable circular orbit
- ISCS: see IRAC Shallow Survey
- ISEE: see International Cometary Explorer
- ISEE-3: see International Cometary Explorer
- iSEEP Wide-Field MAXI: see MAXI
- ISEM: see Rosalind Franklin
- ISG: see rare designator prefixes
- ISGRI: see INTEGRAL
- iShell: see IRTF
- ISI: see Mount Wilson Observatory
- ISIS: see William Herschel Telescope
- ISM (interstellar medium): matter within a galaxy between star systems
- ISM cirrus (infrared cirrus): cirrus-cloud-like infrared emissions from dust, etc.
- ISMF (interstellar magnetic field): galactic magnetic field between that of stars
- ISN (International Supernova Network): SN information sharing initiative
- ISO (Infrared Space Observatory): 1990s 60-cm infrared space telescope
- ISO (International Organization for Standardization): standards-development organization
- ISO spectrum
- ISOCAM: see Infrared Space Observatory
- isochronal fitting: method of estimating stellar age from retrievable parameters
- isochrone: line of equal ages on an HRD
- BaSTI: database relating isochrones to stellar parameters
- H-R diagram: diagram relating effective temperature to luminosity
- isochrone fitting (isochronal fitting): method of estimating stellar age from retrievable parameters
- ISOHDFS: see Hubble Deep Field South
- isolated galaxy (field galaxy): galaxy not in a cluster or group
- isolated neutron star: see neutron star
- isolated planetary mass object (free-floating planet): planet that is not orbiting a star
- isolated planetary mass object: see planetary mass object
- isolated PMO (free-floating planet): planet that is not orbiting a star
- isolation mass: mass of an oligarch after accreting all nearby planetesimals
- isolation mass core: see isolation mass
- isolation mass planet: see isolation mass
- ISON (International Scientific Optical Network): project to track objects in space
- ISOPHOT: see Infrared Space Observatory
- isophote: line on a diagram indicating a level of brightness
- isostasy: crust-mantle equilibrium
- isothermal core: core region of a body of all the same temperature
- isotope: subclass of an element with a specific number of nucleons
- 1H: hydrogen isotope with no neutrons
- deuterium: hydrogen isotope with one neutron
- isotope fractionation: see fractionation
- isotope notation
- isotope: subclass of an element with a specific number of nucleons
- isotope signature: see Moon formation
- isotopes
- element: class of atom based on its number of protons
- mass number: number of nucleons in an atomic nucleus
- nuclide: atomic nucleus associated with a specific isotope
- isotopic fractionation
- isotopic ratio: see abundances
- isotropic radiant energy: see isotropy
- isotropic radiation: see isotropy
- isotropy: uniformity in all directions
- anisotropy: directional-dependence such as temperature variation around the CMB
- ISPM (Ulysses): space mission to observe the Sun from off the ecliptic
- Israeli
- ULTRASAT: future satellite to detect UV transients
- ISRF (interstellar radiation field): EMR throughout the "empty" space of a galaxy
- ISRO (Indian Space Research Organisation): national science and technology agency
- Aditya-L1: 2023 spacecraft viewing Sun and analyzing solar wind
- ISS (IRAC Shallow Survey): Spitzer survey of moderately wide field
- ISS (International Space Station): long-term manned space station operated by numerous nations
- ISS: see Cassini
- ISS: see Voyager
- ISS: see scintillometry
- AMS-02: particle detector on ISS
- COSIE: EUV spectrograph to analyze the corona
- EUSO-SPB: balloon-borne cosmic ray observatory
- MAXI: Japanese X-ray camera on the International Space Station
- NICER: space X-ray mission specifically to view neutron stars
- ISTeC (International Small Telescope Cooperative): former cooperative of small research telescopes
- Istituto di Astrofisica e Planetologia Spaziali: Italian astrophysical research institute within INAF
- Istituto di Astrofisica Spaziale: former name of Italian astrophysics research institution
- Istituto Nazionale di Astrofisica: Italian astrophysical research institute
- ISW: see Sachs-Wolfe effect
- IsWe: see rare designator prefixes
- ISY (International Space Year): 1992 initiative re space and astronomy
- ITA (Institute of Theoretical Astronomy): former Cambridge U astronomy research organization
- ITA (Institute of Theoretical Astrophysics): Heidelberg research institute
- Italian
- Italian National Institute of Astrophysics
- Italian Robotic Antarctic Infrared Telescope (Infrared Telescope Maffei): 80 cm infrared telescope in Antarctica
- Italian Space Agency (Agenzia Spaziale Italiana): includes space-based astronomy research
- AGILE: Italian space gamma-ray observatory
- Italy
- ITCZ (intertropical convergence zone): circulation pattern near equator where north and south Hadley cells meet
- ITEP
- ITEP-SAI Supernova Light Curve Catalogue: online catalog
- iterative method
- ITM (Infrared Telescope Maffei): 80 cm infrared telescope in Antarctica
- Itokawa
- Hayabusa2: JAXA mission that returned a sample of an asteroid
- ITU: international body coordinating communications technology
- IUCAA (Inter-University Centre for Astronomy and Astrophysics): initiative promoting astrophysics at Indian universities
- IUE (International Ultraviolet Explorer): 1980s ultraviolet space telescope
- IUE Data Analysis Center: see International Ultraviolet Explorer
- IUEDAC: see International Ultraviolet Explorer
- IUV: see MAVEN
- IV
- subgiant: slightly larger than normal star
- IV Zw: see Catalog of Galaxies and Clusters of Galaxies
- Ivanov: see rare designator prefixes
- IVC: see high-velocity cloud
- IWA (International Workshop for Astronomy): organization operating the IAYC
- IWCA (International Workshop on Cometary Astronomy): occasional meeting
- iWF-MAXI: see MAXI
- Ixion
- IXO: see ROSAT
- IXPE: space observatory with X-ray polarimeters
Index